Field-deployable diode-laser-based differential absorption lidar (DIAL) for profiling water vapor

Abstract

Abstract.A field-deployable water vapor profiling instrument that builds on the foundation of the preceding generations of diode-laser-based differential absorption lidar (DIAL) laboratory prototypes was constructed and tested. Significant advances are discussed, including a unique shared telescope design that allows expansion of the outgoing beam for eye-safe operation with optomechanical and thermal stability; multistage optical filtering enabling measurement during daytime bright-cloud conditions; rapid spectral switching between the online and offline wavelengths enabling measurements during changing atmospheric conditions; and enhanced performance at lower ranges by the introduction of a new filter design and the addition of a wide field-of-view channel. Performance modeling, testing, and intercomparisons are performed and discussed. In general, the instrument has a 150 m range resolution with a 10 min temporal resolution; 1 min temporal resolution in the lowest 2 km of the atmosphere is demonstrated. The instrument is shown capable of autonomous long-term field operation -50 days with a > 95 % uptime -under a broad set of atmospheric conditions and potentially forms the basis for a ground-based network of eye-safe autonomous instruments needed for the atmospheric sciences research and forecasting communities.

Advances in Diode-Laser-Based Water Vapor Differential Absorption Lidar

“…The large number of daytime sondes allowed for comparisons with the DIAL during periods of high background solar radiation -the most difficult data collection conditions for the instrument. The mean relative error was less than 10% for all of the radiosonde comparisons, from 300 m to 4 km above ground level [13]. Therefore, data from this field campaign demonstrate the capability of the WV-DIAL to provide accurate measurements of water vapor in continual operation for an extended period of time in a variety of atmospheric conditions.…”

“…BS = beam-splitter; T/R = transmit receive; I/O = input output. This figure appears in the Atmospheric Measurement Techniques article by Spuler et al [13] and is used here with permission from Copernicus publications.…”

“…A schematic is shown in Fig. 1 which appears in the Atmospheric Measurement Techniques article by Spuler et al [13] and contains a more complete description and specifications of the system. Figure 1.…”

“…From 2009 to 2012 Nehrir et al significantly advanced the field, particularly with respect to transmitter design [10,11], and subsequently demonstrated the first diode-laser-based WV-DIAL capable of daytime measurements [12]. We have built on these seminal instruments and developed them further -towards a sensor that would be suitable for a national scale network -by improving eye-safety and reliability (e.g., reducing sensitivity to environmental temperature), and enabling accurate measurement of water vapor closer to the ground surface, in rapidly changing atmospheric conditions, and in daytime cloudy conditions up to cloud base [13].…”

Time series analysis of ground-based microwave measurements at K- and V-bands to detect temporal changes in water vapor and temperature profiles

“…Therefore, they cannot be used to detect the temporal variations and gradients in the atmospheric humidity and temperature profiles at regular intervals of time and space. Raman lidars (Goldsmith et al, 1998) and differential absorption lidars (DIAL) (Spuler et al, 2015) are also used during clear sky conditions for sensing humid-ity profiles with a vertical resolution comparable to that of a radiosonde from ground to an altitude of 3 km. Since lidars are quite expensive, they cannot be deployed in a dense network to provide information on spatial distribution and variation on water vapor and temperature.…”